Failure to establish calls upon request from subscribers results in significant loss of revenue to the respective communication carrier. Such failures usually result from errors in stored control programs, databases, or network elements themselves such as switches, network control points, signal transfer points, and the like. Clearly, downtime and associated deterioration in customer service quality and lost revenues could be minimized by surveillance techniques that detect at the earliest opportunity the onset and cause of failure.
Current surveillance techniques, effected by maintenance operation systems, detect and segment faults by simply noting the occurrence of a fault and identifying the suspected faulting network element. In addition to effecting such fault detection and segmentation on actual call failures, test calls may be initiated to effect additional fault analysis. For example, test calls may be sent to specific network elements via specific routes for routing verification. For a detailed discussion of Computer Society's First International Computer and Application Conference, pp. 46-50 (1977) and J. Klimowski, Proceedings of the National Electronic Conference, Vol. 32, pp. 308-313 (1978).
In common practice, prior art surveillance techniques simply result in a network element storing data on failures, threshold crossing events or the like. The reported data, commonly referred to as surveillance data, relates only to failures associated with that network element. The network element must then be either polled to retrieve the surveillance data or programmed, at a predetermined threshold level, to report such failures. The surveillance data is limited in nature to failures occurring within the locality of the reporting network element. Accordingly, detailed analysis of the nature and reason for the fault--the underlying cause of failure--cannot be determined for an extended period of time. Specifically, failures resulting from interactions between network elements and stored control programs cannot be analyzed without related information from each network element associated with the failure. In addition, transient problems that occur in the network system disappear long before a complete investigation can be made. Without a history of the call's progress prior to its failure, a cause of failure which is transient may never be determined. While routing verification techniques test the integrity of a specific route, these techniques likewise result in limited information and add additionally to traffic congestion.
Both the prior art and the invention may in certain embodiments relate to techniques for transmitting signaling information on a "network" which is independent of the communication network, such as common channel signaling. Consequently, a better appreciation of the invention will be gained from the following discussion of common channel signaling.
Common channel signaling has resulted in large part from the increased demand for advanced services such as ISDN and other digital services. Common channel signaling is an out-of-band technique for exchanging trunk signaling and other information between stored program controlled nodes over channels separate from those used to carry voice or data signals. Exemplary of such common channel signaling techniques is one which uses the CCITT No. 7 protocol. For a discussion of common channel signaling No. 7 network signaling see G. G. Schanger, IEEE Journal on Selected Areas in Communication, Vol. SAC-4, No. 3, pp. 360-65 (1986), and S. Suzuki et al., Review of the Electrical Communication Laboratories, Vol. 28, No. 1-2, pp. 50-65 (1980).